Exocytosis of neurotransmitters, hormones and other cell secretory products is believed to occur by calcium-dependent fusion of secretory vesicles with the plasma membrane and by subsequent breakage (fission) of the barrier separating the vesicle interior from the extracellular medium. We have continued our study on synexin, a protein we recently discovered, that can cause the formation of pentalaminar complexes between adjacent chromaffin granule membranes and chromaffin cell plasma membranes in a Ca (II)-dependent manner. This protein may regulate the fusion step in exocytosis, and we have found the activity in a number of secretory organs. More evidence has been accumulated supporting the concept that the fission step in exocytosis may be energized by local osmotic lysis of the fused secretory granule. Finally, evidence that phosphorylation events may be of importance in secretion, at least in cholinergic terminals, has been obtained.